1. Field of the Invention
This invention relates generally to catalytic sweetening of sour hydrocarbons and, more specifically, this invention relates to a method of making a supported metal phthalocyanine oxidation catalyst for oxidizing mercaptans in petroleum distillates.
2. Description of Related Technology
Processes for the treatment of sour petroleum distillates using oxidation catalysts in the presence of suitable oxidizing agents are widely practiced in the petroleum refining industry. These oxidation processes, generally referred to as distillate sweetening, are typically designed to oxidize undesired mercaptans into innocuous disulfides. A wide range of petroleum distillate products, including gasoline, naphtha, kerosene, jet fuel, fuel oil, and lubricating oil, may benefit by the catalytic oxidation of unwanted mercaptans.
An efficient system of oxidizing mercaptans in sour petroleum distillates includes the step of contacting the distillate with a metal chelate catalyst which is supported on a high surface area adsorptive material. Suitable metal chelates and supports include metal phthalocyanine compounds and activated charcoals, respectively. An alkaline agent and an oxidizing agent are typically present when using phthalocyanine catalysts. Generally, the oxidizing agent is air and the alkaline agent is aqueous caustic solution.
U.S. Pat. No. 2,988,500 (Jun. 13, 1961) to Gleim et al. describes a process of catalytically oxidizing petroleum distillates with a metal phthalocyanine catalyst composited on a carbon support. The preferred process treats the petroleum distillate with a an aqueous alkaline agent.
U.S. Pat. No. 3,108,081 (Oct. 22, 1963) to Gleim et al. describes the preparation of a catalytic composition of a support material and a phthalocyanine catalyst. The catalyst is preferably a sulfonated metal phthalocyanine compound deposited on an activated carbon support. The catalyst composition is prepared by soaking the support with an aqueous solution of the sulfonated metal phthalocyanine compound. The solution is usually alkaline, as alkalinity aids the solubility of the sulfonated phthalocyanine compound. Excess solution is removed and the composite is then dried. The alkaline solubility of sulfonated phthalocyanine compounds is problematic because the compounds are leached from the support when alkaline agents are used to treat the petroleum distillates during the oxidation process.
Gleim et al. U.S. Pat. No. 3,108,081 also describes forming the catalyst composition within the treating zone of a distillate reactor. However, the chemical structure of the sulfonated metal phthalocyanine catalyst is not modified by the composition formation, but rather is established before contact with the support.
U.S. Pat. No. 3,230,180 (Jan. 18, 1966) to Larson describes a method of preparing a metal phthalocyanine catalyst combined with or deposited on a solid adsorbent carrier material. The preparation involves depositing a metal oxide on the solid adsorbent and subsequently heating the deposited metal oxide with phthalonitrile at an elevated temperature of 175.degree. to 325.degree. C. The phthalonitrile may be heated with the metal oxide with or without the use of an inert organic solvent.
U.S. Pat. No. 4,248,694 (Feb. 3, 1981) to Carlson et al. describes a process of impregnating charcoal particles with an aqueous solution of a metal phthalocyanine and then wetting the impregnated charcoal with an aqueous metal hydroxide. The metal phthalocyanine is somewhat soluble in the alkaline wetting solution and is therefore susceptible to being leached from the charcoal. Any catalyst leached from the charcoal may be recycled, although it is desirable to introduce additional catalyst for adsorption on the charcoal support to compensate for loss of catalyst therefrom. Mixtures of cobalt phthalocyanine mono- and disulfonates are preferred catalysts. The chemical structure of the phthalocyanine catalyst is established before impregnating the support and is not chemically modified by the described catalyst preparation process.
U.S. Pat. No. 4,364,843 (Oct. 4, 1982) to Carlson describes a catalytic composite prepared from an alcoholic mixture containing less than 25 wt. % water, a metal chelate, an alkali metal hydroxide, and an adsorptive support. The mixture is preferably dried at a temperature of less than 30.degree. C. Methanol containing less than 1 wt. % water is preferably used to form the alcoholic mixture. This procedure, therefore, requires, handling and removing quantities of flammable and costly solvents.